/* eslint-disable */
let buf: any
let bufIdx = 0
const hexBytes = new Array(256)

// Pre-calculate toString(16) for speed
for (let i = 0; i < 256; i++) {
  hexBytes[i] = (i + 0x100).toString(16).substr(1)
}

// Use best available PRNG
const randomBytes = (() => {
  // Node & Browser support
  const lib =
    typeof crypto !== 'undefined' ? crypto : typeof window !== 'undefined' ? window.crypto : void 0

  if (lib !== void 0) {
    if (lib.getRandomValues !== void 0) {
      return (n: number) => {
        const bytes = new Uint8Array(n)
        lib.getRandomValues(bytes)
        return bytes
      }
    }
  }

  return (n: number) => {
    const r = []
    for (let i = n; i > 0; i--) {
      r.push(Math.floor(Math.random() * 256))
    }
    return r
  }
})()

// Buffer random numbers for speed
// Reduce memory usage by decreasing this number (min 16)
// or improve speed by increasing this number (try 16384)
const BUFFER_SIZE = 4096

export default function () {
  // Buffer some random bytes for speed
  if (buf === void 0 || bufIdx + 16 > BUFFER_SIZE) {
    bufIdx = 0
    buf = randomBytes(BUFFER_SIZE)
  }

  const b = Array.prototype.slice.call(buf, bufIdx, (bufIdx += 16))
  b[6] = (b[6] & 0x0f) | 0x40
  b[8] = (b[8] & 0x3f) | 0x80

  return `${hexBytes[b[0]] + hexBytes[b[1]] + hexBytes[b[2]] + hexBytes[b[3]]}-${hexBytes[b[4]]}${
    hexBytes[b[5]]
  }-${hexBytes[b[6]]}${hexBytes[b[7]]}-${hexBytes[b[8]]}${hexBytes[b[9]]}-${hexBytes[b[10]]}${
    hexBytes[b[11]]
  }${hexBytes[b[12]]}${hexBytes[b[13]]}${hexBytes[b[14]]}${hexBytes[b[15]]}`
}
